On prem file server with no domain controller

Look into Azure File Sync, you still need a domain controller for authentication but you could map the file share directly:
https://docs.microsoft.com/en-us/azure/storage/file-sync/file-sync-deployment-guide?tabs=azure-portal%2Cproactive-portal
https://docs.microsoft.com/en-us/azure/storage/files/storage-how-to-use-files-windows.